Laser Spectroscopy Lab.
Laser Spectroscopy Lab.
Our current research
interests are:
1.
Realization
of a CNOT gate using 7Li atom trapped in a 1D optical lattice
We demonstrated in 2014 that broadening of
a ground hyperfine transition for an alkali-metal atom in an
optical trap due to differential ac Stark shift could be
eliminated by using a “magic” polarization. For 7Li, we
obtained 0.6-Hz linewidth and coherence time close to 1 s.
Using the long coherence time and similarity of 7Li to 9Be+ we
are trying to realize a 7Li-CNOT gate following the protocol
of Wineland’s experiment 20 years ago.
2.
New cooling
schemes for a zero-entropy system of 87Rb atoms in a 1D
optical lattice
We started a new experiment to cool 87Rb
atoms to 3D ground vibrational state in a 1D optical lattice.
We also aim to have one and only one atom at each site over
100 consecutive sites so that they constitutes a zero-entropy
system well suited for initial state for quantum information
processings. Our approach is based on evaporative cooling
using selective removal of high-energy atoms and
motion-selective coherent population trapping, which is
analogous to the well-known velocity-selective CPT cooling
scheme.
3.
Atom-interferometer Gyroscope using a slow atomic beam
Using 87Rb atom from a low-velocity-intense
source, we are constructing an atom interferometer gyroscope.
This work is supported by Agency of Defense Development of
Korea.
4.
Precise
displacement-measurement using an optoelectronic oscillator
It is a common practice to measure a small
displacement using a Michelson interferometer. When power
change due to a displacement is measured, it is called a
homodyne detection. When two frequencies are used to produce a
beating signal, a displacement can appear as a phase shift,
and it is called a heterodyne detection. In our experiment we
combined a Michelson interferometer with an optoelectronic
oscillator so that a displacement produces a frequency shift.
During last 20 years
our research has been focused on an optical dipole trap. Some
of the representative results are:
1.
Analogous
Zeeman effect:
With proper detuning and polarization, an
ac Stark shift of a ground-state alkali-metal atom takes the
form of a pure Zeeman shift. We used it to demonstrate (i) an
optical trap that behaves like a magnetic trap, (ii) optical
Stern-Gerlach effect, where light intensity gradient played
the role of a static magnetic field gradient of the landmark
experiment, and (iii) optical Faraday effect.
2.
Magic
wavelength for cesium D2 transition in an optical trap
We pointed out that at 935 nm, differential
ac Stark shift for Cs D2 transition disappears due to the
three-level structure of 6S-6P-5D. We experimentally
demonstrated it in 2003.
3.
Magic
polarization for lithium ground hyperfine transition in an
optical trap
We pointed out that with a proper
polarization, ac Stark shift induced by a vector
polarizability could be tuned to eliminate differential shift
by a scalar polarizability in 2007. This scheme works best
with lithium due to its small fine structure. We demonstrated
a sub-Hz linewidth and a coherence time approaching 1 s using
7Li in an optical trap in 2014.
4.
Transformation of a 1D optical lattice to a traveling-wave
trap
We formed an optical lattice in a
Fabry-Perot cavity. By producing sidebands at plus and minus
one free spectral range away from the carrier, we could
average out the axial intensity gradient at central region of
the lattice.
Welcome to Laser Spectroscopy Laboratory at Department of Physics, Korea University. LSL is an experimental atomic physics group led by Prof. Donghyun Cho since 1994.
Location:
Prof) 409, Asan Science Bldg., 145, Anam-ro, Seongbuk-gu Seoul, 02841 Korea (tel. 02-3290-3102)
Lab) B105, Asan Science Bldg., 145, Anam-ro, Seongbuk-gu Seoul, 02841 Korea (tel. 02-923-2865)